This invention relates to an apparatus for filtration wherein a liquid containing a suspended substance is filtered through a filter bed formed of a packed granular filtering material and, when the filterability of said filter bed is decreased to a fixed extent, the granular filtering material of the filter bed is washed to recover the filterability for filtration.
As a technique for accomplishing the filtration of a liquid by passing the liquid through a filter bed formed of a granular filtering material, there has been known a method whereby the liquid subjected to treatment is passed as a downflow through the filter bed formed of packed granular filtering material to a height of 60 to 200cm, for example.
In this method of filtration, the suspended matter in the liquid is seized mainly in the surface zone of the filter bed and, when the accumulation of the suspended matter in the surface zone has progressed to a certain degree, the overall filterability of the filter bed is abruptly degraded notwithstanding that the suspended matter has not been adsorbed appreciably in the inner zone of the bed. Consequently, the granular filtering material is required to be washed frequently. In the case of a liquid which contains a suspended matter at a high concentration, the filtration becomes extremely difficult. Further, this method requires a special member for supporting the filter bed in position and needs a large filtration tank which makes the filtration efficiency per unit quantity of the filtering material extremely low.
With a view to improving the filtering efficiency, there have been developed a two-bed downflow type filteration apparatus incorporating a filter bed formed of two layers of anthracite and sand and an upflow type filteration apparatus adapted to have a liquid passed as an upflow through the filter bed. These apparatuses have improved the filtering efficiency per unit quantity of filtering material.
In such static filter beds as mentioned above, however, the suspended matter which is seized by the filtering material forms mud balls. These mud balls persist despite all attempts to wash them away and consequently the filtered liquid is degraded in terms of purity.
Various methods resorting to forceful projection of water, aerial agitation and the like have found popular acceptance. Nevertheless, they possess a disadvantage that they are quite expensive and entail consumption of large volumes of water. They provide effects of a passing nature and fail to give a radical solution to the problem.
A principal object of this invention is to provide an apparatus for filtration which has high filtering efficiency per unit quantity of filtering material.
Another object of this invention is to provide an apparatus for filtration which permits easy removal of mud balls and enables the filtration to be efficiently carried out at all times.
Still another object of this invention is to provide an apparatus for filtration which is capable of providing highly efficient filtration to all kinds of liquids.
It is also an object of this invention to provide an apparatus for filtration which provides desired filtration continuously and with high efficiency at all times.